Heat responsive cable



Aug. 15, 1950 F. w. JACKSON 2,518,789

HEAT RESPONSIVE CABLE Filed Sept. 9, 1948 .Jizaem 071 dv fl Patented Aug. 15, 1950 UNITED STATES PATENT OFFICE.

HEAT RESPONSIVE CABLE Frank W. Jackson, Chicago, 111., assignor of onehalf to Harry M. Nacey, Chicago, IlL.

Application September 9, 1948, Serial No. 48,497

(Cl. 2ll0-14 3)- 5 Claims. 1

The invention relates generally to electrical cables and, more particularly to a heatresponsive cable for actuating fire alarm circuits, sprinkler circuits and the like.

The present invention has among its objects, the production of a heat responsive cable in which standard types of wire conductors may be emplayed in. the manufacture thereof, so that the same is relatively inexpensive to manufacture and is very eflicient in operation.

Another object of the invention is the production of such a cable in which the number and size of the elements are reduced to a minimum and a substantially uniform cable is produced.

A further object of the invention is the production of such a cable utilizing a fusible electrically conducting material wherein a maximum amount of such material may be employed without increasing the size of the cable and insuring efficient operation of the cable upon the applica tion of heat thereto.

Many other objects and advantages of the construction herein shownand described will. be obvious tothose skilled in the art from the disclosure herein given.

To this end my invention. consists in the novel construction, arrangement and combination of parts; herein shown and described, and more particularly pointed out in the claims.

In the drawing, wherein like reference characters indicate like or corresponding parts:

Fig. 1 is-a diagrammatic view of a: simple alarm system utilizing the present invention;

Fig. 2 is a plan view of a cable embodying the present invention with portions of the insulation and other elements broken away to disclose the construction thereof; and

Fig, 3 is a: sectional viewthrough the cable illustrated in Fig. 2 taken approximately on the line 3-3 of Fig. 2.

Thepresent invention contemplates the use of two conductors of copper or othersuitablematerial which is relatively flexible, the conductors being electrically insulated from one another by suitable insulatin material, which is respon ive to-the application-of heat, whereby'the insulation will break down, in combination with a fusible electrically conducting; material such as solder or the like. Thus, upon the application of heat to: thecable, the insulation will break down and the electrically conducting material will fuse to provide a direct electrical connection between thetwoconductors at the point-of the insulation breakdown.

Referring toFig. 1., l indicates generally asectionof cable embodying the present invention having two conductors 2 and 3- therein, the conductor 2 for illustrative purposes being connected to one side 4 of an alarm bell 5 or the like, and the conductor 3 operatively connected by a cond-uctcr E2 to one. side of a battery 'i, the opposite side of the battery being connected by a conduc tor 8 to the other-side 9 of the alarm bell 5. Thus, as the conductors 2 and 3 are normally insulated from one another, the bell circuit may be open but upon application of, heat to the cable and an electrical connection made between the conductors 2' and 3' thereof, the circuit will be closed to actuate the-bellE. Gbviously, the cable illustrated may be used in various circuit applications.

As illustrated in Figs. 2 and 3, the conductors 2' and. 3 of tlrecablemaybe twisted together, in which case either one or both may be twisted relative to the other; The solid conductor 2 is provided with a coating of insulation ll, which may be of any suitable electrically n-onconducting material having the desired heat characteristics, ofwhich there are numerous types including rubber, cellulose, etc; I have found that cellulose compositions, as for example, ethyl cellulose lacquer is suitable for the purpose, and is coated upon the wire in a sumcient thickness to provide the desired insulation. The conductor 3, as illustrated in Fig. 3, is of the stranded type made up of a plurality of strands 3 and is impregnated by dipping or the like, with a fusible metal solder [-21 to form. in effect a composite solid conductor, the twoconductors 2 and being covered, if desired, by a suitable woven sheath The coating of insulation l, on the conductor 2, and the fusible metal. l2, on the conductor 3, are both so selected that their heat responsive characteristics are approximately the same whereby the insulation material will break down and. expose. the conductor 2 at substantially the same temperature that the conducting material I2 willfuse and flow between the two conductors, thus electrically connecting the same and closing the alarm or other circuit. Thus, by proper selection of these materials, cables of various critical heat responsive characteristics may be obtained, whereby the circuits may be closed, for example, at 160 to 212, etc. It will. be noted that while the electrical connection between the tWo conductors may be by contact, a direct connection is made by the flowing of the fusiblemetal between, the two conductors,. consequentlvsuch connection is not dependent upon inherent resiliency of the. conductors.

While the cable will function very satisfactorily without an additional sheath l3 enclosing the two conductors, I prefer to employ the sheath l3, making the same from a suitable material having greater heat resistance than the insulating material II, or the conducting material l2, so that the sheath will withstand higher temperatures than that required for breaking down of the insulating material and fusing of the conducting material, whereby the sheath will securely hold the conductors in position as well as forming a receptacle for the fused conducting material, and retain the same adjacent the two conductors and maintain the electrical connection therebetween,

It will be apparent that the interstices between the twisted strands 3 forming the conductor 3 will retain a considerable amount of solder, whereby a stranded conductor carrying the fusible material will carry several times the amount of solder that could be applied to the surface of a solid conductor such as the conductor 2, and assuming that the conductors 2 and 3 are of approximately equal current capacity, the stranded conductor 3 will be slightly larger in overall diameter than the conductor 2. Thus, referring to Fig. 3, it will be noted that the overall diameter of the conductor 2, and coating of insulation I! is approximately equal to the overall diameter of the stranded conductor 3, whereby the finished cable will be substantially uniform in construction and easily bent as desired.

It will also be noted that the present invention embodies only three separate elements, namely, the conductor 2 and its coating of insulation, the conductor 3 carrying the fusible material, and the sheath l3. Similarly, as standard electrical wire may be employed for both of the conductors, a substantially standard sized cable may be produced employing standard machinery and equipment in the fabrication thereof.

I am aware that there have been in the past, numerous cables employing a pair of conductors in combination with a fusible material, and an insulation material normally separating the two conductors. However, all of these cables have generally contemplated the use of concentric conductors, with both the insulation and fusible material concentrically arranged therebetween, or embodying separate fusible strips in conjunction with two insulated conductors. Obviously, such types of cables must be manufactured on special machines and special techniques employed to apply the fusible material and the insulation material to the same conductor particularly if the fusible and insulation materials have similar breakdown temperatures. In contrast to this, is the present construction wherein the insulation material may be readily applied to the solid conductor and the fusible material readily 1. In a heat responsive cable, the combination .4 of a pair of relatively soft, pliable conductors, at least one of said conductors being twisted around the other, one of said conductors being composed of a plurality of twisted strands and having a fusible electrical conducting material filling the interstices between such strands to form a, substantially cylindrical, solid conductor, a coating of insulation on the other conductor electrically insulating the latter from said stranded conductor, said insulation being formed of a material which will break down in response to heat, to permit said fusible conducting material to flow between the conductors and electrically connect the same, and a sheath enclosing said conductors formed from a material requiring greater temperatures for breakdown than said insulation or fusible conducting material.

2. In a heat responsive cable, the combination of a pair of relatively soft, pliable conductors, one of said conductors being composed of a plurality of twisted strands and having a fusible electrical conducting material filling the interstices between such strands to form a substantially cylindrical, solid conductor, and a coating of insulation on the other conductor electrically insulating the latter from said stranded conductor, said insulation being formed of a material which will break down in response to heat, to permit said fusible conducting material to flow between the conductors and electrically connect the same.

3. In a heat responsive cable, the combination of a pair of relatively soft, pliable conductors, at least one of said conductors being twisted around the other, one of said conductors being composed of a plurality of twisted strands and having a fusible electrical conducting material filling the interstices between such strands to form a substantially cylindrical, solid conductor, and a coating of insulation on the other conductor electrically insulating the latter from said stranded conductor, said insulation being formed of a material which will break down in response to heat, to permit said fusible conducting material to flow between the conductors and electrically connect the same.

4. In a heat responsive cable, the combination of a pair of relatively soft, pliable conductors, at least one of said conductors being twisted around the other, one of said conductors being composed of a plurality of twisted strands and having a fusible electrical conducting material filling the interstices between such strands to form a substantially cylindrical, solid conductor, a relatively thin coating of insulation on the other conductor electrically insulating the latter from said stranded conductor, the over-all diameter of the insulated conductor being approximately equal to the diameter of the solid conductor formed by said strands and fusible material, said insulation being formed of a material which will break down in response to heat, to permit said fusible conducting material to flow between the conductors and electrically connect the same, and a sheath enclosing said conductors formed from a material requiring greater temperatures for breakdown than said insulation or fusible conducting material.

5. In a heat responsive cable, the combination of a pair of relatively soft, pliable conductors of approximately equal current capacity, at least one of said conductors twisted around the other, one of said conductors being composed of a plurality of twisted strands and having a fusible electrical conducting material filling the interstices between such strands to form a substan- 5 tially cylindrical, solid conductor, the other conductor being solid and having a coating of insulation thereon electrically insulatin such solid conductor from said stranded conductor, the over-all diameter of the insulated conductor being approximately equal to the diameter of the solid conductor formed by said strands and fusible material, said insulation being formed of a material which will break down in response to heat, to permit said fusible conducting material to flow between the conductors and electrically connect the same, and a sheath enclosing said conductors formed from a material requiring The following references are of record in the file of this patent:

UNITED STATES PATENTS 10 Number Name Date 733,184 Gould July '7, 1903 2,048,271 Lindsey July 21, 1936 2,185,944

Holmes Jan. 2, 1940 

